Do not freshen ReError

compiler/rustc_infer/src/infer/freshen.rs

@@ -110,17 +110,16 @@ impl<'a, 'tcx> TypeFolder<TyCtxt<'tcx>> for TypeFreshener<'a, 'tcx> {
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
         match r.kind() {
-            ty::ReBound(..) => {
-                // leave bound regions alone
-                r
-            }
+            // Leave bound regions alone, since they affect selection via the leak check.
+            ty::ReBound(..) => r,
+            // Leave error regions alone, since they affect selection b/c of incompleteness.
+            ty::ReError(_) => r,
 
             ty::ReEarlyParam(..)
             | ty::ReLateParam(_)
             | ty::ReVar(_)
             | ty::RePlaceholder(..)
             | ty::ReStatic
-            | ty::ReError(_)
             | ty::ReErased => self.cx().lifetimes.re_erased,
         }
     }

tests/crashes/132882.rs

@@ -1,13 +0,0 @@
-//@ known-bug: #132882
-
-use std::ops::Add;
-
-pub trait Numoid
-where
-    for<N: Numoid> &'a Self: Add<Self>,
-{
-}
-
-pub fn compute<N: Numoid>(a: N) -> N {
-    &a + a
-}

tests/ui/traits/eval-caching-error-region.rs

@@ -0,0 +1,23 @@
+// Regression test for #132882.
+
+use std::ops::Add;
+
+pub trait Numoid: Sized
+where
+    &'missing Self: Add<Self>,
+    //~^ ERROR use of undeclared lifetime name `'missing`
+{
+}
+
+// Proving `N: Numoid`'s well-formedness causes us to have to prove `&'missing N: Add<N>`.
+// Since `'missing` is a region error, that will lead to us consider the predicate to hold,
+// since it references errors. Since the freshener turns error regions into fresh regions,
+// this means that subsequent lookups of `&'?0 N: Add<N>` will also hit this cache entry
+// even if candidate assembly can't assemble anything for `&'?0 N: Add<?1>` anyways. This
+// led to an ICE.
+pub fn compute<N: Numoid>(a: N) {
+    let _ = &a + a;
+    //~^ ERROR cannot add `N` to `&N`
+}
+
+fn main() {}

tests/ui/traits/eval-caching-error-region.stderr

@@ -0,0 +1,33 @@
+error[E0261]: use of undeclared lifetime name `'missing`
+  --> $DIR/eval-caching-error-region.rs:7:6
+   |
+LL |     &'missing Self: Add<Self>,
+   |      ^^^^^^^^ undeclared lifetime
+   |
+   = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
+help: consider making the bound lifetime-generic with a new `'missing` lifetime
+   |
+LL |     for<'missing> &'missing Self: Add<Self>,
+   |     +++++++++++++
+help: consider introducing lifetime `'missing` here
+   |
+LL | pub trait Numoid<'missing>: Sized
+   |                 ++++++++++
+
+error[E0369]: cannot add `N` to `&N`
+  --> $DIR/eval-caching-error-region.rs:19:16
+   |
+LL |     let _ = &a + a;
+   |             -- ^ - N
+   |             |
+   |             &N
+   |
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
+   |
+LL | pub fn compute<N: Numoid>(a: N) where &N: Add<N> {
+   |                                 ++++++++++++++++
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0261, E0369.
+For more information about an error, try `rustc --explain E0261`.